Early male touch fastener products were generally woven materials, with hooks formed by cut filament loops. More recently, arrays of very small touch fastener elements have been formed by molding the fastener elements, or at least the stems of the elements, of resin forming an interconnecting sheet of material. Arrays of male fastener elements have also been formed contiguously with a sheet-form base by extruding profile rails with a thicker base, slitting the rails with transverse slits to form rows of discrete fastener elements, and then stretching the base to separate the fastener elements within each row. Such a method is referred to in the industry as ‘cut-and-stretch.’
Molding and/or extrusion enables fastener elements to be formed with stems that taper from a relatively wide base up to the crooks that engage loops, resulting in better lateral stability. Both of these methods are generally much more cost-effective than weaving methods, and can be employed to create extremely small, densely-spaced hooks.
To be molded in blind, fastener element-shaped molding cavities, the fastener element shape must allow for ‘demolding’ the fastener element, such as by pulling it from its cavity without opening the cavity. Cut-and-stretch methods, on the other hand, do not require such shape considerations, but are generally limited, in present practice, to creating fastener elements with flat, parallel, cut faces.
Both methods are useful for forming double-headed fastener elements, each with two heads that face in generally opposite directions. Such hooks are known in the industry as ‘palm tree’ type fastener elements. With cut-and-stretch, the heads tend to extend across the fastener tape, perpendicular to the extrusion direction, while continuous molding methods, such as taught by Fisher, U.S. Pat. No. 4,775,310, are most efficient at forming palm tree hooks with heads that face in the longitudinal material flow direction.
In most applications, male fastener elements are designed to releasably engage with a mating female fastener component carrying a field of loops or fibers. To engage the loops, the male fastener elements must penetrate the field of fibers at least until the tips of the engaging fastener element heads have sufficiently extended beyond some of the fibers, such that the fibers can be engaged within the crooks of the heads. Thus, enhancing penetration tends to lead to longer, more slender hooks.
Subsequent to engagement, retention of an engaged fiber or loop depends, at least for loads within the ability of the loop to resist breakage, upon resistance of the hook to distention and/or breakage. Distention is the opening of the crook under load of an engaged loop. For high cycle life applications, breakage of either both loops and hooks is undesirable. Thus, the ability of the fastening to resist peel loads in such applications is generally limited by the ability of the hook to resist distention.
Further improvements in the overall design of palm tree fastener elements are desired. Preferably, such improved fastener elements will be readily and efficiently manufacturable without great advances in manufacturing methods.